The disclosure relates to an adjusting device which is provided for a hydraulic machine, in particular for a hydraulic axial piston machine, and to a hydraulic axial piston machine, in particular for an axial piston pump, which is configured with an adjusting device of this type.
An axial piston machine of this type is known, for example, from DE 100 01 826 C1. Said axial piston machine which is configured as an axial piston pump has a driving mechanism with a multiplicity of axial pistons which are guided within a cylinder barrel and, together with the latter, in each case delimit a working space. End sections of the pistons on the piston bottom side are supported via sliding pads on a pivot cradle, the pivoting angle of which can be adjusted in order to set the delivery/displacement volume. This adjustment takes place via an adjusting device, an actuating piston acting indirectly or directly on the pivot cradle and pivoting the latter out of a basic position, into which the pivot cradle is prestressed via an opposing cylinder or a spring. In said basic position, the pivot cradle can be set, for example, to its maximum pivoting angle, the pivot cradle then pivoting back by way of extension of the actuating piston. The basic setting to the maximum pivoting angle is advantageous, since, during starting up of the pump, it can immediately deliver a large pressure medium volumetric flow.
In the known solution, the adjusting device for adjusting the pivot cradle is configured as what is known as a power regulator, via which the product of the pressure at the outlet of the pump and the displacement volume is to be kept approximately constant. Strictly speaking, this is a regulation of moment. Power regulation can actually only be spoken of here if the rotational speed is constant.
The actuating piston delimits an actuating space which can be connected via a control valve (what is known as a power regulator) to a line which conducts the pump pressure or to the tank. Said control valve has a control piston which is prestressed via a spring arrangement into a basic position, in which the actuating space is connected to the tank and the actuating piston is therefore retracted. Said spring arrangement is supported on a spring rod which penetrates the control piston and is connected to the actuating piston which is therefore arranged coaxially with respect to the control piston. A differential face is configured on the control piston, which differential face is loaded with the pump pressure, with the result that the control piston can be adjusted counter to the force of the control springs by way of the pump pressure.
In the known solution, the spring arrangement has two springs which are arranged coaxially with respect to one another and of which one comes into engagement only after a certain stroke of the actuating piston, with the result that a p-Q characteristic curve (pressure-delivery flow characteristic curve) is set which consists of two straight lines, the gradient of one straight line being defined by the spring constant of the spring which is first of all in engagement and the gradient of the further straight line being defined by the spring rates of the springs which are jointly in engagement after the part stroke. The optimum hyperbolic p-Q characteristic curve is approximated by way of these two straight lines which are set against one another.
A disadvantage of the known solution is that the adjusting device is of very complex construction on account of the spring rod which penetrates the control piston and, in addition, has a considerable overall length.
DE 40 20 325 C2 discloses a solution, in which a pressure limiting regulator is also assigned to a moment or power regulator of this type.
U.S. Pat. No. 4,379,389 also discloses a solution having two springs, via which the hyperbolic characteristic curve is to be approximated.
In contrast, the disclosure is based on the object of providing an adjusting device and an axial piston machine which is configured with an adjusting device of this type, in which the power/moment regulation is made possible with reduced outlay in terms of device technology.